Rainwater harvesting refers to the collection of rainwater to maximize its environmental and landscape value. Harvesting rainwater
reduces stormwater runoff volume and velocity and can provide an alternative water source to help conserve potable water supplies.
There are typically three components in a rainwater harvesting system: 1) collection; 2) transport; and 3) infiltration or storage
and use.

Collection generally occurs from rooftops or paved surfaces. The collected rainwater is then transported, often through downspouts
or swales, and temporarily held in a storage device for future use. The rainwater also may be diverted to planted areas, such as a
rain garden, for infiltration and use by plants, or directly infiltrated into the soil through permeable paving or an underground
structure such as a dry well. Rainwater harvesting systems are classified as green infrastructure which is targeted at collecting
stormwater to infiltrate and/or store for later use.

Rainwater Uses

Harvested rainwater can be used for potable or non-potable purposes. Non-potable uses include landscape or container plant
irrigation, car washing, and toilet flushing. The use of rainwater in a domestic plumbing system, even for toilet flushing,
requires some form of treatment. Appropriate filtering and disinfection are required for rainwater to be suitable for potable
uses like drinking, cooking, or bathing. This NebGuide only deals with residential-scale rainwater harvesting systems and the use
of captured rainwater for landscape irrigation and other outdoor, non-potable uses.

Why Harvest Rainwater?

Rainwater harvesting has been practiced for centuries and was once a primary method of obtaining water for domestic use.
Increasing water demands, water use restrictions, new stormwater management regulations, and the growth of low-impact development
(LID) and “green building” practices have sparked renewed interest in rainwater harvesting.

In most communities, rainwater is treated as a nuisance and is moved off developed sites as quickly as possible by street gutters,
storm drains, and other means. Public water supplies, treated to drinking water standards, are used for virtually every end use
including toilet flushing, car washing, and landscape irrigation. Although currently the norm, it is not a sustainable practice to
continue using water treated to drinking water standards for non-potable uses. Harvested rainwater can provide an alternative
source to help reduce demand on drinking water supplies.

Rainwater harvesting also has an important role in urban stormwater management. Towns and cities with populations greater than
10,000 are required to reduce the amount of stormwater runoff and associated pollution. Using appropriately sited and installed
rainwater harvesting systems throughout a community will help municipalities with these requirements.

Pollution from Runoff

When rain falls on impervious surfaces such as rooftops, parking lots, streets, driveways, and compacted soils, large quantities
of runoff are generated. This water is generally directed into storm drains and conveyed directly to a stream, river, or lake
without any treatment. In highly urbanized areas, only minimal amounts of precipitation soak into the soil due to the high
percentage of impervious surfaces. This results in a high volume and velocity of concentrated stormwater runoff that can lead to
flooding and polluted surface waters.

Runoff pollution occurs as stormwater flows over surfaces, collecting contaminants like sediment, fertilizer, pesticides,
bacteria, plant debris, metals, fuel, oil, and others. Because most stormwater runoff is not treated before it is discharged to a
waterbody, contaminants are carried directly to surface waters. In addition, runoff to storm drains represents a lost opportunity
to collect and use rainwater as an alternative water source.

Water and Energy Use

Water is essential to life and has no substitute. Population growth, climate change, and other factors are placing greater demand
on fresh water supplies. This increased demand, combined with water pollution, emphasizes the critical need to efficiently use
potable water and to increase the use of alternative sources for non-potable purposes.

In most of the United States, easy access to an abundant, safe, and relatively inexpensive supply of potable water has been the
norm since the last half of the 20th century. Public water supplies are required to meet minimum standards defined by the U.S.
Environmental Protection Agency’s Safe Drinking Water Act. Achieving these standards often involves some form of treatment, and
the water must then be delivered to users through a distribution system. These processes can be energy intensive. Even so, this
high-quality water is used for virtually every end use even though lesser quality water would suffice for some applications. It is
estimated that 40 percent or more of home water use is for landscape irrigation during the growing season. Plants do not require
water that has been treated to drinking water standards. Untreated rainwater is suitable for plant and landscape irrigation.

Benefits of Rainwater Harvesting

Finding and using alternative water sources for landscape irrigation is needed for sustainable water and energy management now and
in the future. The benefits of rainwater harvesting include:

A relatively inexpensive supply of water that needs little or no treatment for most landscape uses.

Rainwater Harvesting Systems With Greenspace

Using greenspace to capture and infiltrate stormwater can be as simple as directing downspouts to planted areas or constructing
small berms and drainage channels (swales) to direct rainwater to planted areas such as shrub borders or tree rows. Eliminating
direct flows to streets and storm drains lessens runoff volumes during storms. However, rain gardens, bioretention gardens,
bioswales, and other planted areas installed specifically to infiltrate stormwater will have greater impact.

A rain garden is an ornamental garden planted in a shallow depression that is designed to hold water for a short time (12-48
hours) before it drains away. These typically have berms on three sides and are located where rainwater from a roof or pavement
can be easily directed to them. Water collected in a properly designed rain garden will infiltrate into the soil for up to 90
percent of all rain events. However, during heavy rain events, water can leave the garden as surface runoff via overflows designed
into the berm. The plants and soil in a rain garden facilitate infiltration and evapotranspiration, as well as provide natural
pollutant filtering (Figure 1).

Bioretention gardens are also ornamental and planted in landscape depressions designed to hold and infiltrate stormwater runoff
within a short period of time. In contrast to rain gardens, bioretention basins are usually larger, have engineered soils
(typically a mixture of sand and compost), and an underdrain system (gravel bed and perforated drain). Collected water infiltrates
into the soil or is discharged through the underdrain into the storm drain system after being filtered by plant roots and soil (Figure 2).

Figure 2. Bioretention garden cross section

A swale is a broad, shallow, gently sloped channel used to convey and infiltrate stormwater. Swales may be lined with vegetation,
gravel or rocks (dry stream bed), compost, rip-rap, or other material. They are designed to slow runoff water velocity, trap
sediment and other contaminants, and promote infiltration. Vegetated swales are also referred to as bioswales, enhanced swales,
grassed swales, or water quality swales (Figure 3).

Stormwater planters are containers typically installed at or beneath street or sidewalk level in which trees and other types of
plants are planted. Runoff is directed into the planter box where it is filtered by soil and vegetation and then discharged into a
storm drain system through an overflow or underdrain. This helps remove pollutants and slows the flow of stormwater entering a
storm drain system (Figure 4).

Green roofs are vegetated roof systems. They commonly consist of drought-tolerant plants, a layer of growing media, a root
barrier, a drainage system, and a waterproof membrane on top of the roof deck. Green roofs directly intercept and absorb
rainwater, provide insulation, and moderate rooftop surface temperatures. They may also extend the life of the roof membrane due
to decreased exposure to temperature extremes, weather, and ultraviolet light. Green roofs can only be installed on buildings with
the structural integrity to support the additional weight (Figure 5).

Figure 3. Bioswale (Lincoln, Neb.)

Figure 4. Stormwater planter (Portland, Ore.)

Figure 5. Green roof (Omaha, Neb.)

Rainwater Harvesting Systems with Permeable Paving

Permeable paving includes several methods and materials used for patio construction and paving driveways, parking lots, and
streets. Examples include pervious concrete, porous asphalt, and permeable pavers such as paving stones or bricks (Figure 6).
Pervious hardscape allows water and air to infiltrate through the surface material into soil or supporting material directly
below. The design may include an underdrain system or an underlying reservoir, tank, or vault for additional water holding
capacity.

Figure 6. Permeable pavers (left); Pervious concrete (right)

Rainwater Harvesting Systems with Storage Devices

Rain barrels are small tanks that store runoff, usually from a roof. Rain barrels are commercially available or adapted from
existing barrels, sit above ground, and typically have a capacity of 55-100 gallons. While rain barrels are a good introduction to
rainwater harvesting, they are limited in the amount of rainwater held. Small water storage units will fill quickly. For this
reason, an overflow to move excess water away from building foundations is needed. Overflow water can be directed to additional
linked storage units, or ideally to a rain garden, bioretention basin, or bioswale (Figure 7).

Cisterns are large (100 gallons or more) tanks for storing collected rainwater. They can be built above or belowground and some
have integrated pumping devices (Figure 8).

Figure 7. Rain barrels with overflow to rain garden (Hastings, Neb.)

Figure 8. 6,000 gallon cistern (Papillion, Neb.)

Bladder tanks are reinforced synthetic bags supported by a metal frame and usually located beneath a deck or porch or in a crawl
space.

Dry wells are permeable underground structures or buried volumes of gravel that store and then slowly release captured rainwater
into the surrounding soil.

Proper use and maintenance of storage devices is essential for safety. Some things to consider are covers to prevent children or
pets from climbing into the container; a secure, level base to prevent tipping of smaller containers; screening to prevent
mosquito entry; and methods to carry overflow away from building foundations.

General Steps to Selecting a Rainwater Harvesting System

Identify areas such as rooftops, paved areas, slopes, or compacted soils from which rainwater could be harvested.

Calculate the amount of rainwater that could be harvested from each area.

Determine the square footage of each collection area.

Multiply the square footage of the area by a rainfall amount in inches; then multiply by 0.623 (a conversion factor).
Example: Harvested water (in gallons) = collection area (square feet) x rainfall amount (inches) x 0.623. A 1,200 square
foot roof would yield approximately 750 gallons of water from a 1 inch rain.

Estimate the square footage of the roof area that would drain to the downspout from which rainwater would be collected to
calculate the potential amount that will flow from that downspout.

3. Calculate the required capacity (size) a rainwater harvesting system needs to be to catch and store enough rainwater from
the site.

4. Evaluate the amount of maintenance each rainwater harvesting system requires and your willingness and ability to properly
monitor and maintain the system.

5. Based on these evaluations, consider which type of system (or multiple systems) to use for harvesting rainwater from the
site.

6. Analyze the suitability of the site specifically for the harvesting system(s) being considered.

Observe drainage patterns during rainfall events. Understand where the water comes from and where it goes. Using natural
drainage to direct and move water simplifies installation and may reduce costs.

Consider how rainwater will be moved from the collection area to an infiltration area.

Determine soil type and understand how water moves into and through it. Conduct a soil percolation test (refer to NebGuide
G1472, Residential Onsite Wastewater Treatment: Conducting a Soil Percolation Test) if an infiltration method is being considered.
A soil infiltration method will not work in every location. For example, infiltration methods may not be appropriate for sites
with slow infiltration rates or where land slopes steeply or towards a building. Minimum distances are also required between
infiltration methods and building foundations, septic systems, and water tables to avoid possible structure damage or water
contamination.

Determine if the installation will negatively affect established trees, shrubs, or neighboring properties as a result of
root disturbances or drastic changes to soil moisture and grade.

7. If a storage method is to be used, determine:

How water would be moved from the collection site to the storage tank.

How the water will be used and how quickly it can be used. (Can the storage unit be emptied before the next predicted
rainfall?)

How and where overflow would be directed when there is heavy rainfall or when rainstorms occur in close succession to one
another.

8. Before installing any rainwater harvesting system, become knowledgeable about:

Homeowner association rules.

State and local municipal codes and regulations.

Underground utility locating services.

Potential incentive programs for using rainwater harvesting methods.

Summary

Renewed interest in rainwater harvesting has come about due to the ever increasing need to maintain and improve fresh water
resources. Rainwater harvesting represents an opportunity to conserve water and help protect surface waters from pollution and
erosion. By using rainwater harvesting systems, it is possible to take advantage of rainwater as an alternative source of water
for non-potable uses; thereby also conserving drinking water and energy.